1. Field of the Invention
The present invention relates to an image pickup apparatus, and more specifically, to an image pickup apparatus such as a digital still camera or a video camera which is able to correct a color signal of a particular color in a video signal.
2. Description of the Related Art
There is an apparatus such as a digital camera capable of automatically performing various settings such as focus and white balance and correcting a color signal of a particular color in a video signal into a predetermined color appropriate for a scene where an image is to be taken, by selecting an image taking mode according to the scene where an image is to be taken (for example, a sea, a night view, a portrait and a landscape).
In addition, as to this apparatus capable of correcting a particular color in a video signal, an image processing device or the like has been invented wherein the this apparatus corrects a particular color into a suitable color which humans latently memorize and feel to be the most beautiful, i.e., a color in human's memory. (For example, refer to Patent Document 1: Japanese Laid-Open Patent JPA-2001-292390).
In this apparatus, for example, when taking an image of a landscape containing a blue sky, the blue color (particular color) of the actually taken image is corrected in to a blue color in human's imagination (blue color in human's memory), because more vivid blue color is usually imagined than an actually viewing color of the blue sky, thereby reproducing the image in a color which agrees with the intention of the photographer (such as a color in human's memory).
An outline of the color correction processing operation of correcting a particular color in the video signal of a taken image will be described below.
FIG. 11 is one example of a block diagram showing a schematic construction of essential units for performing color signal correction processing in a conventional image pickup apparatus, and in which an image pickup apparatus 100A is provided with an image pickup lens unit 101A, an image pickup element 102A, a S/H (Sample & Hold) circuit 103A, an AGC (Automatic Grain Control) circuit 104A, an A/D (Analog to Digital) conversion circuit 105A, a particular color signal extraction circuit 106A, a WB (White Balance) circuit 107A, a gamma correction circuit 108A, a signal processing circuit 109A, a color difference signal correction circuit 110A, an image taking mode selection circuit 120A, a color correction value setting circuit 130A, and the like.
An outline of the operation of color correction processing in the image pickup apparatus 100A having this construction will be described below with reference to the flowchart of FIG. 12.
First, when a photographer selects a desired image taking mode (for example, a sea, a night view, a portrait or a landscape) via the image taking mode selection circuit 120A, predetermined units of the apparatus automatically perform various settings such as focus and white balance according to the image taking mode selected by the image taking mode selection circuit 120A in step ST10.
Table data of color correction values for correcting particular colors are set in the color correction value setting circuit 130A, and the color correction value setting circuit 130A selects a color correction value for a corresponding particular color from among these table data according to the selected image taking mode, and sets the selected color correction value in the color difference signal correction circuit 110A in step ST11 and ST12.
When the image taking is started, light from an object which is inputted into the image pickup lens unit 101A is converted to electrical signals by the image pickup element 102A, and thus obtained electrical signals are converted to digital video signals R[red], G[green], and B[blue] by the A/D conversion circuit 105A through the S/H circuit 103A and the AGC circuit 104A.
The particular color signal extraction circuit 106A extracts a video signal of a particular color from the digital video signal transmitted from the A/D conversion circuit 105A, and calculates a control amount for white balance appropriate for the extracted video signal of the particular color and transmits the control amount to the WB (White Balance) circuit 107A in step ST13.
The WB (White Balance) circuit 107A determines the color temperature of the video signals R[red], G[green], and B[blue] transmitted from the A/D conversion circuit 105A, and corrects the white balance of the video signals R[red], G[green], and B[blue] on the basis of the control amount for the white balance transmitted from the particular color signal extraction circuit 106A, and transmits the corrected video signals R[red], G[green], and B[blue] to the gamma correction circuit 108A. The gamma correction circuit 108A corrects the gray scale of this video signals and transmits the obtained video signals to the signal processing circuit 109A in step ST14 and ST15.
The signal processing circuit 109A converts the digital video signals R[red], G[green], and B[blue] transmitted from the gamma correction circuit 108A to a luminance signal Y and a color difference signal [B-Y] and a color difference signal [R-Y], and outputs the luminance signal Y and also transmits the converted color difference signal [B-Y] and the color difference signal [R-Y] to the color difference signal correction circuit 110A in step ST16.
The color difference signal correction circuit 110A corrects, on the basis of the color correction value which is set by the color correction value setting circuit 130A, a particular color of the color difference signal [B-Y] and the color difference signal [R-Y] transmitted from the signal processing circuit 109A into a predetermined color (such as a color in memory), and transmits the color-corrected color difference signals [B-Y]″ and color difference signal [R-Y]″ to the next-stage circuit in step ST17 and ST18.
The case where a particular color α is color-corrected into a predetermined color α1 by the operation of this color correction processing will be described below by way of example.
When one of image taking modes is selected by the image taking mode selection circuit 120A, the color correction value setting circuit 130A selects from the table data a color correction value for correcting the particular color α corresponding to the selected image taking mode, and sets the selected color correction value in the color difference signal correction circuit 110A.
Specifically, as shown in FIG. 13A, the color correction value is given as a color correction matrix made of parameter values (coefficient values) which are precisely amounts Gain B and Gain R of correction in a direction of gain relative to the particular color and amounts Hue B and Hue R of correction in a direction of hue relative to the same.
For example, if the color correction value is given as parameter values which are precisely the amounts Gain B→“1.5” and Gain R→“1.0” of correction in the direction of gain relative to the particular color and the amounts Hue B→“−0.5” and Hue R→“0.0” of correction in the direction of hue relative to the same, the color correction value (color correction matrix) as shown in FIG. 13B is obtained.
These color correction values are set in the color difference signal correction circuit 110A, and as shown in FIG. 13C, the color correction processing is performed by linearly converting the color difference signal [B-Y] and the color difference signal [R-Y] transmitted from the signal processing circuit 109A by using the color correction values (in a color correction matrix).
For example, in a color difference plane graph as shown in FIG. 13D, the color difference signals [B-Y]″ and the color difference signal [R-Y]″ in which the particular color α (b, r) contained in the color difference signal [B-Y] and the color difference signal [R-Y] is converted to the predetermined color α1 (b″, r″).
In this manner, a particular color of a video signal is color-corrected into a predetermined color according to the selected image taking mode, thereby being used to reproduce an image with a color which agrees with the intention of the photographer (such as a color in human's memory).
However, the conventional image pickup apparatus has the problem that when one of image taking modes is selected, since a color correction value (color correction amount) for correcting a particular color is fixedly selected and set, the particular colors are not necessarily corrected into preferable colors on occasion under any image taking situations or with respect to any taken images.
To cope with this problem, as an improvement measure, the present applicant has filed an patent application (Japanese Patent Application No. 2003-88060) for an image pickup apparatus which extracts a video signal of a particular color from a video signal on the basis of an image taking mode information, detects color difference data on the particular color from the extracted video signal of the particular color, selects correction reference data on a corresponding particular color from correction reference data storage means on the basis of the image taking mode information, calculates a color correction value for correcting the corresponding particular color into a predetermined color on the basis of the selected correction reference data and the color difference data on the particular color detected by color detecting means, and corrects the particular color of the video signal into the predetermined color on the basis of the calculated color correction value.
Similarly, the present applicant has filed an patent application (Japanese Patent Application No. 2003-90611) for an image pickup apparatus which is provided with color convergence parameter storage means which stores color convergence parameter values containing: position data indicating the position of a predetermined color on a color difference plane; correction area setting data for setting as a correction area a predetermined area centered at the position of the predetermined color; and convergence coefficient data for converging a particular color corresponding to the correction area to a position indicative of the predetermined color, and which, on the basis of selected image taking mode information, selects and sets a color convergence parameter value of the corresponding particular color from the color convergence parameter storing means, and converges a particular color in a video signal to a position indicative of a predetermined color on a color difference plane by using a correction amount calculated on the basis of the set color convergence parameter value, thereby effecting color correction.